1. Field of the Invention
This invention relates to carbon nanotube-based sensors, and more particularly to sensors utilizing carbon nanotubes functionalized with a protein sequence containing a peptide recognition element.
2. Description of the Related Art
Carbon nanotubes are cylindrical tubes consisting entirely of carbon and are members of the fullerene structural family. The structure may be a single-walled carbon nanotube (SWNT), meaning that the nanotube wall comprises a single, one-atom thick layer of carbon arranged in a honeycomb crystal lattice, or it may be a multi-walled carbon nanotube comprising multiple layers of carbon tubes nested within one another. The small size and large surface area of carbon nanotubes allows them to possess unique electrical and mechanical properties, such as high thermal and electrical conductivity and high tensile strength. These unique properties have been used to develop rapid-response, SWNT-based sensors that are extremely sensitive, accurate, and lightweight.
Early carbon nanotube-based sensors took advantage of the SWNT's high propensity for molecular adsorption to create sensors that monitor the change in the nanotubes' electrical conductivity upon adsorption of a gas or liquid. However, these sensors generally possess poor selectivity as to the type of molecule adsorbed so that almost any gas or liquid alters the nanotubes' properties, thereby limiting the utility of these sensors.
More recently developed nanotube-based sensors possess increased selectivity due to chemical modification of the nanotubes or the application of functional coatings to the nanotube surface. These modifications to the SWNTs and the SWNT surface allow for increased selectivity and enhanced detection of specific chemical and biological species, while also reducing the amount of non-specific binding and adsorption that occurs. Nanotube-based sensors functionalized with naturally occurring biomolecules, such as enzymes and antibodies/antigens, often require an auxiliary mechanical or chemical linking mechanism to attach the functionalizing agent to the nanotube. The biomolecule alone is usually unable to bind to both the SWNT and the target molecule. In addition, many biomolecules are susceptible to loss of biological activity upon binding to a substrate such as a carbon nanotube and also to instability and degradation upon environmental exposure.